1. Field of the Invention
The present invention relates to a cable with a coating layer made from a waste material.
More particularly, the present invention relates to a cable including at least one core comprising at least one transmissive element and at least one coating layer, said coating layer being made from a coating material comprising at least one polyethylene obtained from a waste material.
Moreover, the present invention relates to a process for producing said cable.
For the purposes of the present description and of the subsequent claims, the term “core” of a cable is used to indicate a semi-finished structure comprising a transmissive element, such as an electrical energy transmissive element, an optical signal transmissive element or an element which both transmits both electrical energy and optical signals, and at least one electrical isolation or, respectively, at least one containment element (such as, for example, a tube, a sheath, a microsheath or a grooved core), or at least two elements, one of which is an electrical isolation element and one is a containment element, arranged at a radially outer position with respect to the corresponding transmissive element.
For the purposes of the present description and of the subsequent claims, the term “electrical energy transmissive element” is used to indicate any element capable of transmitting electrical energy such as, for example, a metallic conductor element. As an illustrative example, if we consider a cable for transporting or distributing medium/high voltage electrical energy (where medium voltage indicates a voltage comprised between about 1 kV and about 30 kV, whereas high voltage indicates a voltage greater than about 30 kV), the “core” of the cable further comprises an inner semiconductive coating layer arranged at a radially outer position with respect to the conductor element, an outer semiconductive coating layer arranged at a radially outer position with respect to the electrical isolation element, a metallic screen arranged at a radially outer position with respect to said outer semiconductive coating layer, and an external layer arranged at a radially outer position with respect to said metallic screen.
For the purposes of the present description and of the subsequent claims, the term “optical signal transmissive element” is used to indicate any transmission element comprising at least one optical fibre. Therefore, such a term identifies both a single optical fibre and a plurality of optical fibres, optionally grouped together to form a bundle of optical fibres or arranged parallel to each other and coated with a common coating to form a ribbon of optical fibres. As an illustrative example, if we consider an optical cable the “core” of the cable further comprises a coating layer arranged at a radially outer position with respect of the grooved core, a tensile reinforcing layer at a radially outer position with respect to said outer coating layer, and an external layer arranged at a radially outer position with respect to said tensile reinforcing layer.
For the purposes of the present description and of the subsequent claims, the term “mixed electro-optical transmissive element” is used to indicate any element capable of transmitting both electrical energy and optical signals in accordance with the abovementioned definitions.
For the purposes of the present description and of the subsequent claims, the term “coating layer” means any coating deposited on the transmissive element of a cable for protective purposes, e.g. to preventing the damages of the transmission element due to mechanical stresses during manufacturing, installation and use.
The present inventions also refers to cables provided with a plurality of cores as defined above, known in the field with the terms “bipolar cable”, “tripolar cable” and “multipolar cable”, depending on the number of cores incorporated therein (in the mentioned cases in number of two, three, or greater, respectively).
In accordance with the abovementioned definitions, the present invention refers to cables provided with one or more cores of any type. In other words, the present invention refers to unipolar or multipolar cables, of electrical type for transporting or distributing electrical energy, or of the optical type comprising at least one optical fibre, or of the mixed energy/telecommunications type.
2. Description of the Related Art
Nowaday, the possibility of using polymer obtained from waste materials for the manufacturing of new products, is a problem of increasing importance for ecological reason and for reducing costs.
In the field of cables, some efforts have been already done in order to use recycled polymer materials, in particular polyvinyl chloride or ethylene polymers obtained from waste cable sheaths. Said recycled polymer materials are generally used for making cable coating layers.
For example, JP 2002/080671 discloses a polyvinyl chloride-based recycled plastic composition obtained by mixing and melting covering plastics and sheaths of waste cables containing: (A) polyvinyl chloride and (B) polyethylene or silane-crosslinked polyethylene, with chlorinated polyethylene. The abovementioned polyvinyl chloride-based resin is said to be useful for making cable sheaths.
JP 2001/098124 relates to a thermoplastic resin composition and to an electrical cable covered with said composition. The thermoplastic resin composition comprises: (A) 1-99 parts by weight of a resin composition containing a polyvinyl chloride resin and a polyethylene resin, said polyvinyl chloride resin and polyethylene resin obtained from waste electrical cables; and (B) 1-99 parts by weight of a multiphase graft copolymer containing (i) 5%-99% by weight of thermoplastic elastomeric units and (ii) 1%-95% by weight of vinyl polymer units where one of the units form a dispersed phase with a particle size of between 0.001 μm-10 μm in the other units. The abovementioned resin composition is said to have a good flexibility and processability when used as an insulating layer or sheath for a cable.
JP 2002/363364 relates to a recycled polyvinyl chloride resin composition comprising a plasticizer having a molecular weight of at least 500 such as, for example, a trimellitate-based, a polyester-based or an epoxy-based plasticizer. The abovementioned composition is said to be useful as covering materials for electrical cables.
JP 2002/363363 relates to a recycled polyvinyl chloride-containing resin composition and to an electrical wire or cable made therefrom. Said composition comprises 100 parts by weight of a 99:1 to 70:30 mixture of a polyvinyl chloride resin which typically is a recycled material and a polyolefin resin, and 1-20 parts by weight with respect to 100 parts by weight of said mixture, of a block copolymer of an acrylic polymer and a hydrogenated polybutadiene in a ratio of 50:50 to 10:90. The abovementioned composition is said to be useful as a covering material for wires and cables.
JP 2002/103329 relates to a method for recycling used vinyl films (e.g. polyvinyl chloride films) for agriculture. The method comprises cutting the used vinyl films roughly; removing impurities such as metals and sand from cut pieces; feeding dried fluff obtained by grinding, washing, dehydrating, and drying said pieces, a plasticizer, a heat stabilizer, and other additives to a heater mixer; keading them; feeding the mixture in a semi-molten state to a cooler mixer; stirring it feeding it to an extruder; extruding it under heated conditions; passing trough a water bath; and pelletizing it. The obtained pellets are dried to form a compound for molding the electrical cable sheath material. Said electrical cable is said to have good properties comparable to a cable having a virgin polyvinyl chloride sheath.
However, the use of recycled polymers may show some drawbacks. In particular, the Applicant has noticed that the use of recycled polyethylene may provide coating layers having poor mechanical properties, in particular stress at break and elongation at break, and poor environmental stress cracking resistance, with respect to those obtained from virgin polymer materials. Moreover, said coating layers may show poor appearance, mainly due to the formation of defects on their surface such as, for example, little agglomerates, which impair not only their appearance and smoothness but also their mechanical properties.
The Applicant believes that the above drawbacks may be due to partial degradation of polyethylene upon prolonged exposure to sunlight and to atmospherical agents, and/or to reprocessing to which said polyethylene is subjected, such degradation causing worsening of mechanical properties and processability.